anything over 45 50 mph in fwd can mess up your hubs or you gears in the rear end i drive a 97 chevy z 71 and i did the same thing your doing and the machanic that had to go through and rebuild my fwd sestem said that your fwd is if you happen to get stuck not for daily driving the auto fwd is fine if u have it because if your back wheels hang up or get stuck it automaticly inuages the front and when the back starts spinning again the front disenguages